1. Field of the Invention
The present invention relates generally to treatment of acidic industrial wastewater and, more particularly, to minimizing precipitation in reverse osmosis systems utilized to treat wastewater.
2. Discussion of the Related Art
Wastewater associated with phosphate manufacturing operations is typically acidic and typically has fluoride, ammonia, silica, sulfate, calcium, heavy metal and phosphate species. Various techniques have been utilized to reduce the level of such contaminants before wastewater can be discharged. For example, the double liming process, followed by air stripping, is a technique that is typically used. It utilizes lime addition in two stages, to promote precipitation of fluoride species and phosphate species, followed by high pH, air stripping to remove ammonia. In another technique, wastewater has been treated by techniques involving chemical precipitation followed by reverse osmosis. Like the double liming process, such techniques raise the pH of influent wastewater to promote precipitation and solids separation before the reverse osmosis step. The high chemical costs typically associated with raising the pH of the wastewater make such processes economically unattractive.